Polymerizable compositions comprising nanoparticles

ABSTRACT

Polymerizable compositions comprising nanopartilces particularly useful for brightness enhancing films.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/662,085 filed Sep. 12, 2003; a continuation-in-part of U.S.patent application Ser. No. 10/870,366 filed Jun. 17, 2004; acontinuation-in-part of U.S. patent application Ser. No. 10/939,184,filed Sep. 10, 2004; and a continuation-in-part of U.S. patentapplication Ser. No. 10/938,006, filed Sep. 10, 2004.

BACKGROUND

Certain microreplicated optical products, such as described in U.S. Pat.Nos. 5,175,030 and 5,183,597, are commonly referred to as a “brightnessenhancing films”. Brightness enhancing films are utilized in manyelectronic products to increase the brightness of a backlit flat paneldisplay such as a liquid crystal display (LCD) including those used inelectroluminescent panels, laptop computer displays, word processors,desktop monitors, televisions, video cameras, as well as automotive andaviation displays.

Brightness enhancing films desirably exhibit specific optical andphysical properties including the index of refraction of a brightnessenhancing film that is related to the brightness gain (i.e. “gain”)produced. Improved brightness can allow the electronic product tooperate more efficiently by using less power to light the display,thereby reducing the power consumption, placing a lower heat load on itscomponents, and extending the lifetime of the product.

Brightness enhancing films have been prepared from high index ofrefraction monomers that are cured or polymerized, as described forexample in U.S. Pat. Nos. 5,908,874; 5,932,626; 6,107,364; 6,280,063;6,355,754; as well as EP 1 014113 and WO 03/076528.

Although various polymerizable compositions that are suitable for themanufacture of brightness enhancing films are known, industry would findadvantage in alternative compositions.

SUMMARY

In one embodiment, a brightness enhancing film having a brightnessenhancing polymerized structure is described that comprises the reactionproduct of a polymerizable composition comprising

-   at least about 15 wt-% of one or more first monomers selected from-   i) a monomer comprising a major portion having the structure    -   wherein R1 is independently hydrogen or methyl,    -   R2 is independently H or Br,    -   Z is independently —C(CH₃)₂—, —CH₂—, —C(O)—, —S—, —S(O)—, or        —S(O)₂—, and    -   Q is independently O or S;-   ii) a monomer comprising a major portion having the structure    -   wherein R1 is independently hydrogen or methyl,    -   R2 is independently H or Br,    -   Z is independently —C(CH₃)₂—, —CH₂—, —C(O)—, —S—, —S(O)—, or        —S(O)₂—, and    -   L is a linking group independently selected from linear and        branched C₂-C₁₂ alkyl groups wherein the carbon chain is        optionally substituted with one or more oxygen group and/or the        carbon atoms are optionally substituted with one or more        hydroxyl groups;-   and mixtures of i) and ii);-   b) at least about 10 wt-% inorganic nanoparticles; and-   c) optionally a crosslinking agent comprising at least three    (meth)acrylate functional groups.

In another embodiment, a brightness enhancing film having a brightnessenhancing polymerized structure is described that comprises the reactionproduct of a polymerizable composition comprising

-   a) at least about 15 wt-% of one or more (meth)acrylated aromatic    epoxy oligomers;    -   b) at least about 10 wt-% inorganic nanoparticles; and    -   c) optionally a crosslinking agent comprising at least three        (meth)acrylate functional groups.

In another embodiment, a brightness enhancing film having a brightnessenhancing polymerized structure is described that comprises the reactionproduct of a substantially solvent free polymerizable compositioncomprising an organic component, comprising one or more ethylenicallyunsaturated monomers, and at least 10 wt-% inorganic nanoparticles. Theorganic component has a viscosity of less than 1000 cps at 180° F. Theorganic component may comprise at least one oligomeric ethylenicallyunsaturated monomer having a number average molecular weight of greaterthan 450 g/mole.

In yet another embodiment, a brightness enhancing film having abrightness enhancing polymerized structure is described that comprisesthe reaction product of a substantially solvent free polymerizablecomposition comprising an organic component comprising one or moreethylenically unsaturated monomers wherein the organic component has arefractive index of at least 1.54; and at least 10 wt-% inorganicnanoparticles.

The amount of inorganic particles is typically less than about 60 wt-%.The inorganic nanoparticles are preferably surface modified. Theinorganic nanoparticles typically comprise silica, zirconia, titania,antimony oxides, alumina, tin oxides, mixed metal oxides thereof, andmixtures thereof. The nanoparticles may range in primary particle sizefrom 5 nm to 75 nm, from 10 nm to 30 nm, from 5 nm to 15 nm.

The first monomer preferably consists of the reaction product ofTetrabromobisphenol A diglycidyl ether and (meth)acrylic acid. Thepolymerizable compositions may further comprise at least one second highindex monomer (i.e. different than the first monomer). The polymerizablecomposition is preferably free of methacrylate functional monomer.

In other embodiments, the invention relates to an article comprising thebrightness enhancing film in contact with a second optical film or lightguide. The second optical film may include a turning film, a diffuser,an absorbing polarizer, a reflective polarizer, or a protective coverfilm.

The polymerizable compositions described herein may also be advantageousfor other optical or microstructured articles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an illustrative microstructure-bearingoptical product of the present invention.

FIG. 2 is a schematic view of an illustrative backlit liquid crystaldisplay including the brightness enhancing film of the invention.

DETAILED DESCRIPTION

As used within the present description:

“Index of refraction,” or “refractive index,” refers to the absoluterefractive index of a material (e.g., a monomer) that is understood tobe the ratio of the speed of electromagnetic radiation in free space tothe speed of the radiation in that material. The refractive index can bemeasured using known methods and is generally measured using an Abberefractometer in the visible light region (available commercially, forexample, from Fisher Instruments of Pittsburgh, Pa.). It is generallyappreciated that the measured index of refraction can vary to someextent depending on the instrument.

“(Meth)acrylate” refers to both acrylate and methacrylate compounds.

“Polymerizable composition” refers to the total composition includingthe organic component that comprises at least one polymerizable monomerand the optional inorganic nanoparticles.

“Organic component” refers to all of the components of the compositionexcept for the inorganic nanoparticles. For embodiments wherein thepolymerizable composition is free of inorganic nanoparticles, theorganic component and polymerizable composition are one in the same.

The term “nanoparticles” is defined herein to mean particles (primaryparticles or associated primary particles) with a diameter less thanabout 100 nm.

“Surface modified colloidal nanoparticle” refers to nanoparticles eachwith a modified surface such that the nanoparticles provide a stabledispersion.

“Aggregation” refers to a strong association between primary particlesthat may be chemically bound to one another. The breakdown of aggregatesinto smaller particles is difficult to achieve.

“Agglomeration refers to a weak association between primary particleswhich my be held together by charge or polarity and can be broken downinto smaller entities.

“Primary particle size” refers to the mean diameter of a single(non-aggregate, non-agglomerate) particle.

Brightness enhancing films generally enhance on-axis luminance (referredherein as “brightness”) of a lighting device. Brightness enhancing filmscan be light transmissible, microstructured films. The microstructuredtopography can be a plurality of prisms on the film surface such thatthe films can be used to redirect light through reflection andrefraction. The height of the prisms typically ranges from about 1 toabout 75 microns. When used in an optical display such as that found inlaptop computers, watches, etc., the microstructured optical film canincrease brightness of an optical display by limiting light escapingfrom the display to within a pair of planes disposed at desired anglesfrom a normal axis running through the optical display. As a result,light that would exit the display outside of the allowable range isreflected back into the display where a portion of it can be “recycled”and returned back to the microstructured film at an angle that allows itto escape from the display. The recycling is useful because it canreduce power consumption needed to provide a display with a desiredlevel of brightness.

Brightness enhancing films include microstructure-bearing articleshaving a regular repeating pattern of symmetrical tips and grooves.Other examples of groove patterns include patterns in which the tips andgrooves are not symmetrical and in which the size, orientation, ordistance between the tips and grooves is not uniform. Examples ofbrightness enhancing films are described in Lu et al., U.S. Pat. No.5,175,030, and Lu, U.S. Pat. No. 5,183,597, incorporated herein byreference.

Referring to FIG. 1, a brightness enhancing film 30 may comprise a baselayer 2 and optical layer 4. Optical layer 4 comprises a linear array ofregular right prisms, identified as prisms 6, 8, 12, and 14. Each prism,for example, prism 6, has a first facet 10 and a second facet 11. Theprisms 6, 8, 12, and 14 are formed on base 2 that has a first surface 18on which the prisms are formed and a second surface 20 that issubstantially flat or planar and opposite first surface 18. By rightprisms it is meant that the apex angle α is typically about 90°.However, this angle can range from 70° to 120° and may range from 80° to100°. Further the apexes can be sharp, rounded, flattened or truncated.The prism facets need not be identical, and the prisms may be tiltedwith respect to each other. The relationship between the total thickness24 of the optical article, and the height 22 of the prisms, may vary.However, it is typically desirable to use relatively thinner opticallayers with well-defined prism facets. A typical ratio of prism height22 to total thickness 24 is generally between 25/125 and 2/125.

The base layer of the brightness enhancing film can be of a nature andcomposition suitable for use in an optical product, i.e. a productdesigned to control the flow of light. Many materials can be used as abase material provided the material is sufficiently optically clear andis structurally strong enough to be assembled into or used within aparticular optical product. Preferably, the base material is chosen thathas sufficient resistance to temperature and aging that performance ofthe optical product is not compromised over time.

The particular chemical composition and thickness of the base materialfor any optical product can depend on the requirements of the particularoptical product that is being constructed. That is, balancing the needsfor strength, clarity, temperature resistance, surface energy, adherenceto the optical layer, among others. The thickness of the base layer istypically at least about 0.025 millimeters (mm) and more typically atleast about 0.25 mm. Further, the base layer generally has a thicknessof no more than about 1 mm.

Useful base layer materials include cellulose acetate butyrate,cellulose acetate propionate, cellulose triacetate, polyether sulfone,polymethyl methacrylate, polyurethane, polyester, polycarbonate,polyvinyl chloride, syndiotactic polystyrene, polyethylene naphthalate,copolymers or blends based on naphthalene dicarboxylic acids, and glass.Optionally, the base material can contain mixtures or combinations ofthese materials. For example, the base may be multi-layered or maycontain a dispersed phase suspended or dispersed in a continuous phase.Exemplary base layer materials include polyethylene terephthalate (PET)and polycarbonate. Examples of useful PET films include photogradepolyethylene terephthalate (PET) and PET commercially available fromDuPont Films of Wilmington, Del., under the trade designation “Melinex”.

The base layer material can be optically active, and can act as apolarizing material. A number of base layer materials are known to beuseful as polarizing materials. Polarization of light through a film canbe accomplished, for example, by the inclusion of dichroic polarizers ina film material that selectively absorbs passing light. Lightpolarization can also be achieved by including inorganic materials suchas aligned mica chips or by a discontinuous phase dispersed within acontinuous film, such as droplets of light modulating liquid crystalsdispersed within a continuous film. As an alternative, a film can beprepared from microfine layers of different materials. The polarizingmaterials within the film can be aligned into a polarizing orientation,for example, by employing methods such as stretching the film, applyingelectric or magnetic fields, and coating techniques.

Examples of polarizing films include those described in U.S. Pat. Nos.5,825,543 and 5,783,120, each incorporated herein by reference. The useof these polarizer films in combination with a brightness enhancementfilm has been described in U.S. Pat. No. 6,111,696; incorporated hereinby reference. Another example of a polarizing film is described in U.S.Pat. No. 5,882,774; incorporated herein by reference. Multilayerpolarizing films are sold by 3M Company, St. Paul, Minn. under the tradedesignation DBEF (Dual Brightness Enhancement Film). The use of suchmultilayer polarizing optical film in a brightness enhancement film hasbeen described in U.S. Pat. No. 5,828,488; incorporated herein byreference.

Other polarizing and non-polarizing films can also be useful as the baselayer for brightness enhancing films of the invention such as describedin U.S. Pat. Nos. 5,612,820 and 5,486,949, among others.

The present invention relates to polymerizable resin compositions usefulfor optical articles and in particular the optical layer of a brightnessenhancing film. The brightness enhancing or other microstructuredarticles comprise a polymerized structure comprising the reactionproduct of an organic component optionally comprising a plurality ofnanoparticles. The polymerized structure can be an optical element oroptical product constructed of a base layer and an optical layer. Thebase layer and optical layer can be formed from the same or differentpolymer material.

The polymerizable resin composition comprises a first monomer having arefractive index of at least 1.47, for most product applications;whereas the polymerizable resin composition of a turning film may have arefractive index as low as 1.44. High transmittance in the visible lightspectrum is also typically preferred. The composition of the inventionis preferably polymerizable by irradiation with ultraviolet or visiblelight in the presence of a photoinitiator.

In one embodiment, the invention relates to a polymerizable compositioncomprising a first monomer that comprises a major portion having thefollowing general structures I or II:

In each of structures I and II, each R1 is independently hydrogen ormethyl. Each R2 is independently hydrogen or bromine. Each Z isindependently —C(CH₃)₂—, —CH₂—, —C(O)—, —S—, —S(O)—, or —S(O)₂—, andeach Q is independently O or S. Typically, the R1 groups are the same.Typically, the R2 groups are the same as each other well. In structureII, L is a linking group. L may independently comprise a branched orlinear C₂-C₁₂ alkyl group. The carbon chain of the alkyl group mayoptionally be substituted with one or more oxygen groups. Further, thecarbon atoms of the alkyl group may optionally be substituted with oneor more hydroxyl groups. For example L may be —CH₂CH(OH)CH₂—. Typically,the linking groups are the same. Preferably the alkyl group comprises nomore than 8 carbon atoms and more preferably no more than 6 carbonatoms.

Mixtures of I and II may also be employed.

The first monomer may be synthesized or purchased. As used herein, majorportion refers to at least 60-70 wt-% of the monomer containing thespecific structure(s) just described. It is commonly appreciated thatother reaction products are also typically present as a byproduct of thesynthesis of such monomers.

The first monomer is preferably the reaction product ofTetrabromobisphenol A diglycidyl ether and acrylic acid. The firstmonomer may be obtained from UCB Corporation, Smyrna, Ga. under thetrade designation “RDX-51027”. This material comprises a major portionof 2-propenoic acid,(1-methylethylidene)bis[(2,6-dibromo-4,1-phenylene)oxy(2-hydroxy-3,1-propanediyl)]ester.

Although, mixtures of such first monomers may also suitably be employed,for ease in manufacturing it is preferred to employ as few differentmonomers as possible, yet still attain a brightness enhancing film withsuitable gain. To meet this end, it is preferred that the brightnessenhancing film is comprised of the reaction product of only one of thesefirst monomers and in particular the reaction product ofTetrabromobisphenol A diglycidyl ether and acrylic acid.

In another embodiment, the polymerizable composition comprises at leastone (meth)acrylated aromatic epoxy oligomer. Various (meth)acrylatedaromatic epoxy oligomers are available commercially available. Forexample, (meth)acrylated aromatic epoxy, (described as a modified epoxyacrylates), are available from Sartomer, Exton, PA under the tradedesignation “CN118”, “CN115” and “CN112C60”. An (meth)acrylated aromaticepoxy oligomer, (described as an epoxy acrylate oligomer), is availablefrom Sartomer under the trade designation “CN2204”. Further, an(meth)acrylated aromatic epoxy oligomer, (described as an epoxy novolakacrylate blended with 40% trimethylolpropane triacrylate), is availablefrom Sartomer under the trade designation “CN112C60”.

In some embodiments, the aromatic epoxy acrylate is derived frombisphenol A, such as those of II. In other embodiments, however, thearomatic epoxy acrylate may be derived from a monomer different thanbisphenol A. The organic component may comprise aromatic epoxy acrylate,at least one crosslinking agent, at least one reactive diluent, and atleast one other ethylenically unsaturated monomer. Alternatively, theorganic component of the polymerizable composition may only include thearomatic epoxy acrylate and crosslinking agent or the aromatic epoxyacrylate and reactive diluent, each of such including photoinitiator. Ifan aromatic epoxy acrylate is employed the polymerizable composition,the aromatic epoxy acrylate may be monofunctional provided that thepolymerizable composition includes at least one ingredient thatcomprises at least two ethylenically unsaturated polymerizable groups.The aromatic epoxy acrylate may have three or more (meth)acrylategroups. The aromatic epoxy(meth)acrylate may be halogenated, typicallyhaving a refractive index of greater than 1.56. In other aspects, thearomatic epoxy(meth)acrylate may have a refractive index of less than1.56. The aromatic epoxy(meth)acrylate may have a viscosity of greaterthan 2150 cps at 65° C. Less than 30 wt-% of the aromaticepoxy(meth)acrylate may be employed, for example in combination with areactive diluent. In other embodiments, the aromatic epoxy(meth)acrylate may have a viscosity of less than 2150 cps at 65° C., anddiluent may not be employed. Greater than 30 wt-% of the aromaticepoxy(meth)acrylate may be employed in organic component.

The first monomer and/or aromatic epoxy(meth)acrylate is preferablypresent in the polymerizable composition in an amount of at least about15 wt-% (e.g. 20 wt-%, 30 wt-%, 35 wt-%, 40 wt-%, 45 wt-% and 50 wt-%and any amount there between). Typically, the amount of the firstmonomer and/or aromatic epoxy(meth)acrylate does not exceed about 60wt-%.

In addition to the first monomer and/or aromatic epoxy(meth)acrylate,the polymerizable composition of the invention can optionally include atleast one and preferably only one crosslinking agent. Multi-functionalmonomers can be used as crosslinking agents to increase the glasstransition temperature of the polymer that results from the polymerizingof the polymerizable composition. The glass transition temperature canbe measured by methods known in the art, such as Differential ScanningCalorimetry (DSC), modulated DSC, or Dynamic Mechanical Analysis.Preferably, the polymeric composition is sufficiently crosslinked toprovide a glass transition temperature that is greater than 45° C.

The crosslinking agent comprises at least two (meth)acrylate functionalgroups. Since methacrylate groups tend to be less reactive than acrylategroups, it is preferred that the crosslinking agent comprises three ormore acrylate groups. Suitable crosslinking agents include for examplehexanediol acrylate (HDDA), pentaerythritol tri(meth)acrylate,pentaerythritol tetra(meth)acrylate, trimethylolpropanetri(methacrylate), dipentaerythritol penta(meth)acrylate,dipentaerythritol hexa(meth)acrylate, trimethylolpropane ethoxylatetri(meth)acrylate, glyceryl tri(meth)acrylate, pentaerythritolpropoxylate tri(meth)acrylate, and ditrimethylolpropanetetra(meth)acrylate. Any one or combination of crosslinking agents maybe employed.

The crosslinking agent is preferably present in the polymerizablecomposition in an amount of at least about 2 wt-%. Typically, the amountof crosslinking agent is not greater than about 25 wt-%. Thecrosslinking agent may be present in any amount ranging from about 5wt-% and about 15 wt-%.

Preferred crosslinking agents include hexanediol diacrylate (HDDA),pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate,dipentaerythritol penta(meth)acrylate, trimethylolpropanetri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, andmixtures thereof. More preferably the crosslinking agent(s) is free ofmethacrylate functionality. Pentaerythritol triacrylate (PETA) anddipentaerythritol pentaacrylate are commercially available from SartomerCompany, Exton, Pa. under the trade designations “SR444” and “SR399LV”respectively; from Osaka Organic Chemical Industry, Ltd. Osaka, Japanunder the trade designation “Viscoat #300”; from Toagosei Co. Ltd.,Tokyo, Japan under the trade designation “Aronix M-305”; and fromEternal Chemical Co., Ltd., Kaohsiung, Taiwan under the tradedesignation “Etermer 235”. Trimethylol propane triacrylate (TMPTA) andditrimethylol propane tetraacrylate (di-TMPTA) are commerciallyavailable from Sartomer Company under the trade designations “SR351” and“SR355”. TMPTA is also available from Toagosei Co. Ltd. under the tradedesignation “Aronix M-309”. Further, ethoxylated trimethylolpropanetriacrylate and ethoxylated pentaerythritol triacrylate are commerciallyavailable from Sartomer under the trade designations “SR454” and “SR494”respectively.

For embodiments wherein surface modified nanoparticles having sufficientpolymerizable reactive groups are employed, a crosslinking agent neednot be employed. For example, 10 wt-% phenoxy ethyl acrylate can becombined with the first monomer and at least 10 wt-% of the surfacemodified nanoparticles (e.g. of Example 1).

The (e.g. first, aromatic epoxy(meth)acrylate) monomer(s) as well asoptional crosslinking agent and optional reactive diluent typicallycomprise (meth)acrylate functional groups. In preferred embodiments thepolymerizable composition comprises solely acrylate functionality andthus is substantially free of methacrylate functional groups.

The polymerizable composition described herein contains (e.g. surfacemodified) inorganic oxide particles. The size of such particles ischosen to avoid significant visible light scattering. It may bedesirable employ a mixture of inorganic oxide particle types to optimizean optical or material property and to lower total composition cost.Hybrid polymers formed from inorganic nanoparticles and organic resin isamenable to achieving durability unobtainable with conventional organicresins alone. The inclusion of the inorganic nanoparticles can improvethe durability of the articles (e.g. brightness enhancing film) thusformed.

The polymerizable compositions just described are preferred compositionsfor providing a substantially solvent free polymerizable compositioncomprising inorganic nanoparticles and an organic component, wherein theorganic component has a low viscosity, such as less than 1000 cps at180° F.

“Substantially solvent free” refer to the polymerizable compositionhaving less than 5 wt-%, 4 wt-%, 3 wt-%, 2 wt-%, 1 wt-%, and 0.5 wt-% of(e.g. organic) solvent. The concentration of solvent can be determinedby known methods, such as gas chromatography. Solvent concentrations ofless than 0.5 wt-% are preferred.

The organic component can be a solid or comprise a solid componentprovided that the melting point in the polymerizable composition is lessthan the coating temperature. The organic component can be a liquid atambient temperature.

The components of the organic component are preferably chosen such thatthe organic component has a low viscosity. Typically the viscosity ofthe organic component is substantially lower than the organic componentof compositions previously employed. The viscosity of the organiccomponent is less than 1000 cps and typically less than 900 cps. Theviscosity of the organic component may be less than 800 cps, less than450 cps, less than 600 cps, or less than 500 cps at the coatingtemperature. As used herein, viscosity is measured with 25 mm parallelplates using a Dynamic Stress Rheometer (at a shear rate up to 1000sec-1). Further, the viscosity of the organic component is typically atleast 10 cps, more typically at least 50 cps, even more typically atleast 100 cps, and most typically at least 200 cps at the coatingtemperature.

The coating temperature typically ranges from ambient temperature, (i.e.25° C.) to 180° F. (82° C.). The coating temperature may be less than170° F. (77° C.), less than 160° F. (71° C.), less than 150° F. (66°C.), less than 140° F. (60° C.), less than 130° F. (54° C.), or lessthan 120° F. (49° C.). The organic component can be a solid or comprisea solid component provided that the melting point is less than thecoating temperature. The organic component can be a liquid at ambienttemperature.

The organic component as well as the polymerizable composition has arefractive index of at least 1.47, for most product applications;whereas the polymerizable resin composition of a turning film may have arefractive index as low as 1.44. The refractive index of the organiccomponent or the polymerizable composition may be at least 1.48, 1.49,1.50, 1.51, 1.52, 1.53, 1.54, 1.55, 1.56, 1.57, 1.58, 1.59, or 1.60. Thepolymerizable composition including the nanoparticles can have arefractive index as high as 1.70. (e.g. at least 1.61, 1.62, 1.63, 164,1.65, 1.66, 1.67, 1.68, or 1.69) High transmittance in the visible lightspectrum is also typically preferred.

Accordingly, the polymerizable compositions just described are alsopreferred compositions for providing a substantially solvent freepolymerizable composition comprising nanoparticles and an organiccomponent comprising one or more ethylenically unsaturated monomerswherein the organic component has a high refractive index, i.e. of atleast 1.54.

The polymerizable composition having the low viscosity and/or highrefractive index organic component may be prepared from otherethylenically unsaturated monomers as well. The organic component maycomprise a (meth)acrylated urethane oligomer, (meth)acrylated polyesteroligomer, a (meth)acrylated phenolic oligomer, a (meth)acrylated acrylicoligomer, and mixtures thereof. In some embodiments, however, theorganic component is free of urethane linkages.

The organic component may comprise at least one oligomeric ethylenicallyunsaturated monomer having a number average molecular weight of greaterthan 450 g/mole, typically in combination with a reactive diluent and/orcrossliker.

Suitable oligomeric (meth)acrylated aromatic epoxy oligomers arecommercially available from Sartomer under the trade designations“CN104”, “CN116”, “CN120”, CN121” and “CN136”; from Cognis under thetrade designation “Photomer 3016”; and from UCB under the tradedesignations “3200”, “3201”, “3211” and “3212”.

Suitable urethane (meth)acrylates are commercially available fromSartomer under the trade designations “CN965”, “CN968”, “CN981”, “CN983”, “CN 984”, “CN972”, and “CN978”; from Cognis under the tradedesignation “Photomer 6210”, “Photomer 6217”, “Photomer 6230”, “Photomer6623”, “Photomer 6891”, and “Photomer 6892”; and from UCB under thetrade designations “Ebecryl 1290”, “Ebecryl 2001”, and “Ebecryl 4842”.

Suitable polyester (meth)acrylates are commercially available fromSartomer under the trade designation “CN292”; from Cognis under thetrade designation “Photomer 5010”, “Photomer 5429”, “Photomer 5430”,“Photomer 5432”, “Photomer 5662”, “Photomer 5806”, and “Photomer 5920”;and from UCB under the trade designations “Ebecryl 80”, “Ebecryl 81”,“Ebecryl 83”, “Ebecryl 450”, “Ebecryl 524”, “Ebecryl 525”, “Ebecryl585”, “Ebecryl 588”, “Ebecryl 810”, and “Ebecryl 2047”.

Suitable phenolic (meth)acrylates are commercially available fromSartomer under the trade designation “SR601” and “SR602”; from Cognisunder the trade designations “Photomer 4025” and “Photomer 4028”.

Suitable (meth)acrylated acrylic oligomers are also commerciallyavailable or can be prepared by methods know in the art.

In each embodiment described herein, the polymerizable resin compositionoptionally, yet preferably comprises up to about 35 wt-% (e.g. integersranging from 1 to 35) reactive diluents to reduce the viscosity of thepolymerizable resin composition and to improve the processability.Reactive diluents are mono-ethylenically unsaturated monomers such as(meth)acrylates or monomeric N-substituted or N,N-disubstituted(meth)acrylamides, especially an acrylamide. These includeN-alkylacrylamides and N,N-dialkylacrylamides, especially thosecontaining C₁₋₄ alkyl groups. Examples are N-isopropylacrylamide,N-t-butylacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide,N-vinyl pyrrolidone and N-vinyl caprolactam.

Preferred diluents can have a refractive index greater than 1.50 (e.g.greater than 1.55. Such reactive diluents can be halogenated ornon-halogenated (e.g. non-brominated). Suitable monomers typically havea number average molecular weight no greater than 450 g/mole include

Suitable reactive diluents include for example phenoxyethyl(meth)acrylate; phenoxy-2-methylethyl(meth)acrylate;phenoxyethoxyethyl(meth)acrylate,3-hydroxy-2-hydroxypropyl(meth)acrylate; benzyl(meth)acrylate,4-(1-methyl-1-phenethyl)phenoxyethyl(meth)acrylate; phenylthio ethylacrylate; 2-naphthylthio ethyl acrylate; 1-naphthylthio ethyl acrylate;2,4,6-tribromophenoxy ethyl acrylate; 2,4-dibromophenoxy ethyl acrylate;2-bromophenoxy ethyl acrylate; 1-naphthyloxy ethyl acrylate;2-naphthyloxy ethyl acrylate; phenoxy 2-methylethyl acrylate;phenoxyethoxyethyl acrylate; 3-phenoxy-2-hydroxy propyl acrylate;2-phenylphenoxy ethyl acrylate; 4-phenylphenoxy ethyl acrylate;2,4-dibromo-6-sec-butylphenyl acrylate; 2,4-dibromo-6-isopropylphenylacrylate; benzyl acrylate; phenyl acrylate; 2,4,6-tribromophenylacrylate.

Other high refractive index monomers such as pentabromobenzyl acrylateand pentabromophenyl acrylate can also be employed.

The inclusion of only one diluent is preferred for ease inmanufacturing. A preferred diluent is phenoxyethyl(meth)acrylate, and inparticular phenoxyethyl acrylate (PEA). Phenoxyethyl acrylate iscommercially available from more than one source including from Sartomerunder the trade designation “SR339”; from Eternal Chemical Co. Ltd.under the trade designation “Etermer 210”; and from Toagosei Co. Ltdunder the trade designation “TO-1166”. Benzyl acrylate is commerciallyavailable from AlfaAeser Corp, Ward Hill, Mass.

Such optional monomer(s) may be present in the polymerizable compositionin amount of at least about 5 wt-%. The optional monomer(s) typicallytotal no more than about 50 wt-% of the polymerizable composition. Thesome embodiments the total amount of optional high index monomer rangesfrom about 30 wt-% to about 45 wt-% (including integers between 30 and45).

The optional high index monomer may be halogenated (i.e. brominated).One exemplary high index optional monomer is2,4,6-tribromophenoxyethyl(meth)acrylate commercially available fromDaiichi Kogyo Seiyaku Co. Ltd (Kyoto, Japan) under the trade designation“BR-31”.

Suitable methods of polymerization include solution polymerization,suspension polymerization, emulsion polymerization, and bulkpolymerization, as are known in the art. Suitable methods includeheating in the presence of a free-radical initiator as well asirradiation with electromagnetic radiation such as ultraviolet orvisible light in the presence of a photoinitiator. Inhibitors arefrequently used in the synthesis of the polymerizable composition toprevent premature polymerization of the resin during synthesis,transportation and storage. Suitable inhibitors include hydroquinone,4-methoxy phenol, and hindered amine nitroxide inhibitors at levels of50-1000 ppm. Other kinds and/or amounts of inhibitors may be employed asknown to those skilled in the art.

The composition of the present invention optionally comprises a leastone photoinitiator. A single photoinitiator or blends thereof may beemployed in the brightness enhancement film of the invention. In generalthe photoinitiator(s) are at least partially soluble (e.g. at theprocessing temperature of the resin) and substantially colorless afterbeing polymerized. The photoinitiator may be (e.g. yellow) colored,provided that the photoinitiator is rendered substantially colorlessafter exposure to the UV light source.

Suitable photoinitiators include monoacylphosphine oxide andbisacylphosphine oxide. Commercially available mono or bisacylphosphineoxide photoinitiators include 2,4,6-trimethylbenzoydiphenylphosphineoxide, commercially available from BASF (Charlotte, N.C.) under thetrade designation “Lucirin TPO”; ethyl-2,4,6-trimethylbenzoylphenylphosphinate, also commercially available from BASF under the tradedesignation “Lucirin TPO-L”; andbis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide commercially availablefrom Ciba Specialty Chemicals under the trade designation “Irgacure819”. Other suitable photoinitiators include2-hydroxy-2-methyl-1-phenyl-propan-1-one, commercially available fromCiba Specialty Chemicals under the trade designation “Darocur 1173” aswell as other photoinitiators commercially available from Ciba SpecialtyChemicals under the trade designations “Darocur 4265”, “Irgacure 651”,“Irgacure 1800”, “Irgacure 369”, “Irgacure 1700”, and “Irgacure 907”.

The photoinitiator can be used at a concentration of about 0.1 to about10 weight percent. More preferably, the photoinitiator is used at aconcentration of about 0.5 to about 5 wt-%. Greater than 5 wt-% isgenerally disadvantageous in view of the tendency to cause yellowdiscoloration of the brightness enhancing film. Other photoinitiatorsand photoinitiator may also suitably be employed as may be determined byone of ordinary skill in the art.

Surfactants such as fluorosurfactants and silicone based surfactants canoptionally be included in the polymerizable composition to reducesurface tension, improve wetting, allow smoother coating and fewerdefects of the coating, etc.

The polymerizable compositions are energy curable in time scalespreferably less than five minutes such as for a brightness enhancingfilm having a 75 micron thickness. The polymerizable composition ispreferably sufficiently crosslinked to provide a glass transitiontemperature that is typically greater than 45° C. The glass transitiontemperature can be measured by methods known in the art, such asDifferential Scanning Calorimetry (DSC), modulated DSC, or DynamicMechanical Analysis. The polymerizable composition can be polymerized byconventional free radical polymerization methods.

Although inorganic nanoparticles lacking polymerizable surfacemodification can usefully be employed, the inorganic nanoparticles arepreferably surface modified such that the nanoparticles arepolymerizable with the organic component. Surface modified (e.g.colloidal) nanoparticles can be present in the polymerized structure inan amount effective to enhance the durability and/or refractive index ofthe article or optical element. The surface modified colloidalnanoparticles described herein can have a variety of desirableattributes, including for example; nanoparticle compatibility with resinsystems such that the nanoparticles form stable dispersions within theresin systems, surface modification can provide reactivity of thenanoparticle with the resin system making the composite more durable,properly surface modified nanoparticles added to resin systems provide alow impact on uncured composition viscosity. A combination of surfacemodifiers can be used to manipulate the uncured and cured properties ofthe composition. Appropriately surface modified nanoparticles canimprove the optical and physical properties of the optical element suchas, for example, improve resin mechanical strength, minimize viscositychanges while increasing solid volume loading in the resin system andmaintain optical clarity while increasing solid volume loading in theresin system.

The surface modified colloidal nanoparticles can be oxide particleshaving a primary particle size or associated particle size of greaterthan 1 nm and less than 100 nm. It is preferred that the nanoparticlesare unassociated. Their measurements can be based on transmissionelectron miscroscopy (TEM). The nanoparticles can include metal oxidessuch as, for example, alumina, tin oxides, antimony oxides, silica,zirconia, titania, mixtures thereof, or mixed oxides thereof. Surfacemodified colloidal nanoparticles can be substantially fully condensed.

Non-silica containing fully condensed nanoparticles typically have adegree of crystallinity (measured as isolated metal oxide particles)greater than 55%, preferably greater than 60%, and more preferablygreater than 70%. For example, the degree of crystallinity can range upto about 86% or greater. The degree of crystallinity can be determinedby X-ray defraction techniques. Condensed crystalline (e.g. zirconia)nanoparticles have a high refractive index whereas amorphousnanoparticles typically have a lower refractive index.

Silica nanoparticles can have a particle size from 5 to 75 nm or 10 to30 nm or 20 nm. Silica nanoparticles can be present in the durablearticle or optical element in an amount from 10 to 60 wt-%, or 10 to 40wt-%. Silicas for use in the materials of the invention are commerciallyavailable from Nalco Chemical Co., Naperville, Ill. under the tradedesignation “Nalco Collodial Silicas” such as products 1040, 1042, 1050,1060, 2327 and 2329. Suitable fumed silicas include for example,products commercially available from DeGussa AG, (Hanau, Germany) underthe trade designation, “Aerosil series OX-50”, as well as productnumbers -130, -150, and -200. Fumed silicas are also commerciallyavailable from Cabot Corp., Tuscola, I, under the trade designationsCAB-O-SPERSE 2095”, “CAB-O-SPERSE A105”, and “CAB-O-SIL M5”.

Zirconia nanoparticles can have a particle size from 5 to 50 nm, or 5 to15 nm, or 10 nm. Zirconia nanoparticles can be present in the durablearticle or optical element in an amount from 10 to 70 wt-%, or 30 to 60wt-%. Zirconias for use in composition and articles of the invention areavailable from Nalco Chemical Co. under the trade designation “NalcoOOSSOO8” and from Buhler AG Uzwil, Switzerland under the tradedesignation “Buhler zirconia Z-WO sol”. Zirconia nanoparticle can alsobe prepared such as described in U.S. patent application Ser. No.11/027,426 filed Dec. 30, 2004 and U.S. Pat. No. 6,376,590.

Titania, antimony oxides, alumina, tin oxides, and/or mixed metal oxidenanoparticles can have a particle size or associated particle size from5 to 50 nm, or 5 to 15 nm, or 10 nm. Titania, antimony oxides, alumina,tin oxides, and/or mixed metal oxide nanoparticles can be present in thedurable article or optical element in an amount from 10 to 70 wt-%, or30 to 60 wt-%. Mixed metal oxide for use in materials of the inventionare commercially available from Catalysts & Chemical Industries Corp.,Kawasaki, Japan, under the trade designation “Optolake 3”.

Surface-treating the nano-sized particles can provide a stabledispersion in the polymeric resin. Preferably, the surface-treatmentstabilizes the nanoparticles so that the particles will be welldispersed in the polymerizable resin and results in a substantiallyhomogeneous composition. Furthermore, the nanoparticles can be modifiedover at least a portion of its surface with a surface treatment agent sothat the stabilized particle can copolymerize or react with thepolymerizable resin during curing.

The nanoparticles of the present invention are preferably treated with asurface treatment agent. In general a surface treatment agent has afirst end that will attach to the particle surface (covalently,ionically or through strong physisorption) and a second end that impartscompatibility of the particle with the resin and/or reacts with resinduring curing. Examples of surface treatment agents include alcohols,amines, carboxylic acids, sulfonic acids, phosphonic acids, silanes andtitanates. The preferred type of treatment agent is determined, in part,by the chemical nature of the metal oxide surface. Silanes are preferredfor silica and other for siliceous fillers. Silanes and carboxylic acidsare preferred for metal oxides such as zirconia. The surfacemodification can be done either subsequent to mixing with the monomersor after mixing. It is preferred in the case of silanes to react thesilanes with the particle or nanoparticle surface before incorporationinto the resin. The required amount of surface modifier is dependantupon several factors such particle size, particle type, modifiermolecular wt, and modifier type. In general it is preferred thatapproximately a monolayer of modifier is attached to the surface of theparticle. The attachment procedure or reaction conditions required alsodepend on the surface modifier used. For silanes it is preferred tosurface treat at elevated temperatures under acidic or basic conditionsfor from 1-24 hr approximately. Surface treatment agents such ascarboxylic acids may not require elevated temperatures or extended time.

Representative embodiments of surface treatment agents suitable for thecompositions include compounds such as, for example, isooctyltrimethoxy-silane, N-(3-triethoxysilylpropyl)methoxyethoxyethoxyethylcarbamate, N-(3-triethoxysilylpropyl) methoxyethoxyethoxyethylcarbamate, 3-(methacryloyloxy)propyltrimethoxysilane,3-acryloxypropyltrimethoxysilane,3-(methacryloyloxy)propyltriethoxysilane,3-(methacryloyloxy)propylmethyldimethoxysilane,3-(acryloyloxypropyl)methyldimethoxysilane,3-(methacryloyloxy)propyldimethylethoxysilane, 3-(methacryloyloxy)propyldimethylethoxysilane, vinyldimethylethoxysilane,phenyltrimethoxysilane, n-octyltrimethoxysilane,dodecyltrimethoxysilane, octadecyltrimethoxysilane,propyltrimethoxysilane, hexyltrimethoxysilane,vinylmethyldiacetoxysilane, vinylmethyldiethoxysilane,vinyltriacetoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane,vinyltrimethoxysilane, vinyltriphenoxysilane, vinyltri-t-butoxysilane,vinyltris-isobutoxysilane, vinyltriisopropenoxysilane,vinyltris(2-methoxyethoxy)silane, styrylethyltrimethoxysilane,mercaptopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane,acrylic acid, methacrylic acid, oleic acid, stearic acid, dodecanoicacid, 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEAA),beta-carboxyethylacrylate, 2-(2-methoxyethoxy)acetic acid, methoxyphenylacetic acid, and mixtures thereof. Further, a proprietary silane surfacemodifier, commercially available from OSI Specialties, Crompton SouthCharleston, W. Va. under the trade designation “Silquest A1230”, hasbeen found particularly suitable.

The surface modification of the particles in the colloidal dispersioncan be accomplished in a variety of ways. The process involves themixture of an inorganic dispersion with surface modifying agents.Optionally, a co-solvent can be added at this point, such as forexample, 1-methoxy-2-propanol, ethanol, isopropanol, ethylene glycol,N,N-dimethylacetamide and 1-methyl-2-pyrrolidinone. The co-solvent canenhance the solubility of the surface modifying agents as well as thesurface modified particles. The mixture comprising the inorganic sol andsurface modifying agents is subsequently reacted at room or an elevatedtemperature, with or without mixing. In a preferred method, the mixturecan be reacted at about 85° C. for about 24 hours, resulting in thesurface modified sol. In a preferred method, where metal oxides aresurface modified the surface treatment of the metal oxide can preferablyinvolve the adsorption of acidic molecules to the particle surface. Thesurface modification of the heavy metal oxide may take place at roomtemperature.

The surface modification of ZrO₂ with silanes can be accomplished underacidic conditions or basic conditions. In one preferred case the silanesare preferably heated under acid conditions for a suitable period oftime. At which time the dispersion is combined with aqueous ammonia (orother base). This method allows removal of the acid counter ion from theZrO₂ surface as well as reaction with the silane. In a preferred methodthe particles are precipitated from the dispersion and separated fromthe liquid phase.

The surface modified particles can then be incorporated into the curableresin in various methods. In a preferred aspect, a solvent exchangeprocedure is utilized whereby the resin is added to the surface modifiedsol, followed by removal of the water and co-solvent (if used) viaevaporation, thus leaving the particles dispersed in the polymerizableresin. The evaporation step can be accomplished for example, viadistillation, rotary evaporation or oven drying.

In another aspect, the surface modified particles can be extracted intoa water immiscible solvent followed by solvent exchange, if so desired.

Alternatively, another method for incorporating the surface modifiednanoparticles in the polymerizable resin involves the drying of themodified particles into a powder, followed by the addition of the resinmaterial into which the particles are dispersed. The drying step in thismethod can be accomplished by conventional means suitable for thesystem, such as, for example, oven drying or spray drying.

A combination of surface modifying agents can be useful, wherein atleast one of the agents has a functional group co-polymerizable with ahardenable resin. Combinations of surface modifying agent can result inlower viscosity. For example, the polymerizing group can beethylenically unsaturated or a cyclic function subject to ring openingpolymerization. An ethylenically unsaturated polymerizing group can be,for example, an acrylate or methacrylate, or vinyl group. A cyclicfunctional group subject to ring opening polymerization generallycontains a heteroatom such as oxygen, sulfur or nitrogen, and preferablya 3-membered ring containing oxygen such as an epoxide.

A preferred combination of surface modifying agent includes at least onesurface modifying agent having a functional group that isco-polymerizable with the (organic component of the) hardenable resinand a second modifying agent different than the first modifying agent.The second modifying agent is optionally co-polymerizable with theorganic component of the polymerizable composition. The second modifyingagent may have a low refractive index (i.e. less than 1.52 or less than1.50). The second modifying agent is preferably a polyalkyleneoxidecontaining modifying agent that is optionally co-polymerizable with theorganic component of the polymerizable composition.

As described in Lu and Lu et al., a microstructure-bearing article (e.g.brightness enhancing film) can be prepared by a method including thesteps of (a) preparing a polymerizable composition (i.e. thepolymerizable composition of the invention); (b) depositing thepolymerizable composition onto a master negative microstructured moldingsurface in an amount barely sufficient to fill the cavities of themaster; (c) filling the cavities by moving a bead of the polymerizablecomposition between a preformed base and the master, at least one ofwhich is flexible; and (d) curing the composition. The master can bemetallic, such as nickel, nickel-plated copper or brass, or can be athermoplastic material that is stable under the polymerizationconditions, and that preferably has a surface energy that allows cleanremoval of the polymerized material from the master. One or more thesurfaces of the base film can be optionally be primed or otherwise betreated to promote adhesion of the optical layer to the base.

The brightness enhancing film of the invention is usefully employed in adisplay for the purpose of improving the gain. A schematic view of anillustrative backlit liquid crystal display generally indicated at 110in FIG. 2. In the actual display, the various components depicted areoften in contact with the brightness enhancing film. The brightnessenhancing film 111 of the present invention is generally positionedbetween a light guide 118 and a liquid crystal display panel 114. Theliquid crystal display panel typically includes an absorbing polarizeron both surfaces. Thus, such absorbing polarizer is positioned adjacentto the brightness enhancing film of the invention. The backlit liquidcrystal display can also include a light source 116 such as afluorescent lamp and a white reflector 120 also for reflecting lightalso toward the liquid crystal display panel. The brightness enhancingfilm 111 collimates light emitted from the light guide 118 therebyincreasing the brightness of the liquid crystal display panel 114. Theincreased brightness enables a sharper image to be produced by theliquid crystal display panel and allows the power of the light source116 to be reduced to produce a selected brightness. The backlit liquidcrystal display is useful in equipment such as computer displays (laptopdisplays and computer monitors), televisions, video recorders, mobilecommunication devices, handheld devices (i.e. cell phone, personaldigital assistant (PDA)), automobile and avionic instrument displays,and the like, represented by reference character 121.

The display may further include another optical film 112 positionedbetween the brightness enhancing film and the liquid crystal displaypanel 114. The other optical film may include for example a diffuser, areflective polarizer, or a second brightness enhancing film. Otheroptical films may be positioned between optical film 112 and the liquidcrystal display panel 114 or between the brightness enhancing film 111and the light guide 118, as are known in the art. Further, a turningfilm may be located between lightguide and optical film. Alternatively,the brightness enhancing film may be a turning film. A turning filmtypically includes prism structures formed on an input surface, and theinput surface is disposed adjacent the lightguide. The light raysexiting the lightguide at the glancing angle, usually less than 30degrees to the output surface, encounter the prism structures. The lightrays are refracted by a first surface of the prism structures and arereflected by a second surface of the prism structures such that they aredirected by the turning lens or film in the desired direction, e.g.,substantially parallel to a viewing axis of the display.

Examples of polarizing films include those described in U.S. Pat. Nos.5,825,543 and 5,783,120, each of which are incorporated herein byreference. The use of these polarizer films in combination with abrightness enhancing film has been described in U.S. Pat. No. 6,111,696.Another example of a polarizing film is described in U.S. Pat. No.5,882,774. One example of such films that are available commercially arethe multilayer films sold under the trade designation DBEF (DualBrightness Enhancement Film) from 3M Company. Multilayer polarizingoptical films have been described, for example in U.S. Pat. No.5,828,488. A turning film typically includes prism structures formed onan input surface and the input surface is disposed adjacent to alightguide. The light rays exiting the lightguide at the glancingangles, usually less than 30 degrees to the output surfaces, encounterthe prism structures. The light rays are refracted by a first surface ofthe prism structures and are reflected by a second surface of the prismstructures such that the rays are directed by the turning film in thedesired direction, e.g. substantially parallel to a viewing axis of thedisplay. If these additional optical films are included as the baselayer of the brightness enhancing films, than the thickness of the baselayer may be considerably greater than previously described.

The polymerizable composition described herein may be advantageous forother optical materials such as microstructure-bearing optical articles(e.g. films). Exemplary optical materials include optical lenses such asFresnel lenses, optical films, such as high index of refraction filmse.g., microreplicated films such as totally internal reflecting films,or brightness enhancing films, flat films, multilayer films,retroreflective sheeting, optical light fibers or tubes, flexible molds(e.g. suitable for making barrier ribs for plasma display panels) andothers. The production of optical products from high index of refractionpolymerizable compositions is described, for example, in U.S. Pat. No.4,542,449, the disclosure of which is incorporated herein by reference.

Advantages of the invention are further illustrated by the followingexamples, but the particular materials and amounts thereof recited inthe examples, as well as other conditions and details, should not beconstrued to unduly limit the invention. All percentages and ratiosherein are by weight unless otherwise specified.

EXAMPLES

Test Methods

1. Gain Test Method

Gain, the difference in transmitted light intensity of an opticalmaterial compared to a standard material, was measured on a SpectraScan™PR-650 SpectraColorimeter available from Photo Research, Inc,Chatsworth, Calif. Results of this method for each example formed beloware reported in the RESULTS section below. In order to measure thesingle sheet gain (i.e. “SS”) film samples were cut and placed on aTeflon light cube that is illuminated via a light-pipe using a FosterDCR II light source such that the grooves of the prisms are parallel tothe front face of the Teflon light cube. For crossed sheet gain (i.e.“XS”) a second sheet of the same material is placed underneath the firstsheet and orientated such that the grooves of the second sheet arenormal to the front face of the Teflon light cube.

In three sets of experiments, polymerizable resin compositions wereprepared into brightness enhancing films using a master tool that had a90° apex angles as defined by the slope of the sides of the prisms. Inthe first set of experiments, the mean distance between adjacent apiceswas about 50 micrometers and the apex of the prism vertices was round.In the second set of experiments, the mean distance between adjacentapices was about 50 micrometers and the apex of the prism vertices wassharp. In the third set of experiments, the mean distance betweenadjacent apices was about 24 micrometers and the apex of the prismvertices was sharp. For Experiment 1 (Control 1, Samples 1-3) andExperiment 3 (Control 3, Sample 5), polymerizable resin compositionswere heated to a temperature of about 50° C. and poured onto the mastertool in a sufficient volume to create a continuous film. The master tooland polymerizable resin were pulled through a coating bar device tocreate a thickness of polymerizable resin of approximately 25 microns inthe first set of experiments and approximately 13 microns in the thirdset of experiments. After coating, a PET film was laminated ontopolymerizable resin. The master tool, polymerizable resin, and PET filmwere then placed into UV curing machine and exposed at 3000millijoules/cm². After curing, the polymerized resin and PET were peeledfrom the master tool. Experiment 2 was performed under similar processconditions as described for Experiments 1 & 3, but was conducted in acontinuous fashion.

In the first set of experiments brightness enhancing films were preparedfrom polymerizable resin compositions 1-3 along with a control (i.e.Control 1 of Table I). In a second set of experiments brightnessenhancing films were prepared from polymerizable resin composition 4along with a control (i.e. Control 2 of Table I). In a third set ofexperiments, brightness enhancing films were prepared from polymerizableresin composition 5 along with a control (i.e. Control 3 of Table I).For each set of experiments the control consisted of a mixture of 12.5wt-% PEA, 37.5 wt-% BR-31, 30 wt-% RDX-51027, 20 wt-% of a crosslinkingagent obtained from UCB Corporation under the trade designation“EB-9220”, 1 pph Darocur 1173, and 0.3 wt-% surfactant, commerciallyavailable from 3M Company under the trade designation “FC-430′”.

Table I as follows sets forth the amount of first monomer, kind andamount of monofunctional diluent (i.e. phenoxyethyl acrylate (PEA)),crosslinking agent (i.e. PETA), inorganic nanoparticles, photoinitiator(Lucirin TPO-L) employed in the examples. The first monomer employed inthe examples comprised at least about 60-70 wt-% of 2-propenoic acid,(1-methylethylidene)bis[(2,6-dibromo-4,1-phenylene)oxy(2-hydroxy-3,1-propanediyl)]ester. TABLE I Polymerizable Photo- Wt. % Surface Resin initiator Wt. %First Wt. % Modifier SS XS Composition 1 pph PEA Monomer PETA Wt. %Other Gain Gain Control 1 1.666 Example 1 TPO-L 9.7 29 9.7 5.7 46 wt. %1.552 20 nm SiO2 Example 2 TPO-L 11.5 34.4 11.5 4.7 38 wt. % 1.557 20 nmSiO₂ Example 3 TPO-L 12.8 24.5 12.8 4 32 wt. % 1.570 20 nm SiO₂ Control2 1.707 2.500 Example 4 TPO-L 9.2 27.5 9.2 15 39% Nalco 1.717 2.535zirconia Control 3 1.721 2.488 Example 5 TPO-L 8.6 25.7 8.6 9.1 48%Buhler 1.838 2.496 zirconia Example 6 1.881 2.687*See example for ingredients.

Example 1

Nalco 2327 (400 g) was charged to a 1 qt jar. 1-Methoxy-2-propanol (450g), 3-(trimethoxysilyl)propyl methacrylate commercially available fromSigma-Aldrich, Milwaukee, Wis. under the trade designation “Silane A174”(18.95 g), Silquest A1230 (12.74 g), and a 5% solution in water (0.2 g)of hindered amine nitroxide inhibitor commercially available from CibaSpecialty Chemical, Inc. Tarrytown, N.Y. under the trade designation“Prostab 5198” was prepared and added to a colloidal silica dispersioncommercially available from Ondeo-Nalco Co., Naperville, Ill. under thetrade designation “Nalco 2327” while stirring. The jar was sealed andheated to 80° C. for 16.5 hours. This resulted in a clear, low viscositydispersion of modified silica.

A 1 L round-bottom flask (large neck) was charged with the abovemodified sol (442.23 g), 20/60/20 SR444/First Monomer/PEA (82.25 g) anda 5% solution of Prostab 5198 in water (0.65 g). Water and alcohol wereremoved via rotary evaporation. The formulation contained 46.04 wt %SiO₂ as measured by TGA. Refractive index was 1.512. 1 wt % TPO-L wasadded.

Example 2

The SiO₂ containing resin from Example 1 (10 g) was mixed with 20/60/20SR444/First Monomer/PEA (2.12 g) to give a 38 wt-% SiO₂ containingresin. 1 wt-% TPO-L was added.

Example 3

The SiO₂ containing resin from Example 1 (10 g) was mixed with 20/60/20SR444/First Monomer/PEA (4.38 g) to give a 32 wt-% SiO₂ containingresin. 1 wt % TPO-L was added.

Example 4

Preparation of silane-modified zirconia nanoparticle dispersion: NalcoOOSSOO8 zirconia sol (372.56 g) and 2-[2-(2-methoxyethoxy)ethoxy]aceticacid (MEEAA) commercially available from Sigma-Aldrich (23.16 g) werecharged to a 1 L round bottom flask. The water and acetic acid wereremoved via rotary evaporation. The powder thus obtained was redispersedin 127.58 g D.I water and charged to a 2 L beaker to which was addedwith stirring 400 g 1-methoxy-2-propanol, 36.62 g A-174, 24.61 gSilquest A-1230 and 0.4 g of a 5% solution of Prostab 5198 in water.This mixture was stirred 30 min at room temperature then poured into 1 L(quart) jars, sealed and heated to 90° C. for 3.0 h. The contents of thejars were removed and concentrated to 40% ZrO₂ via rotary evaporation.Deionized water (1565 g) and 51 g concentrated aqueous ammonia (29% NH₃)were charged to a 4 L beaker. The concentrated dispersion (295 g) wasadded slowly to the beaker with stirring. The white precipitate thusobtained was isolated via vacuum filtration and washed with additionalD.I. water. The damp solids were dispersed in 1-methoxy-2-propanol (370g). The resultant silane modified zirconia dispersion contained 20.2%solids.

The above modified ZrO₂ dispersion (540 g), 20/60/20 PEA/FirstMonomer/SR444 (90.4 g) and a 5% solution of Prostab 5198 in water (0.72g) were charged to a 1 L round bottom flask. Water and alcohol wereremoved via rotary evaporation. The resultant formulation contained38.60% ZrO₂ by TGA and had a refractive index of 1.587.

Example 5

Preparation of silane-modified zirconia nanoparticle dispersion: Buhlerzirconia Z-WO sol (401.5 g) (available from Buhler AG Uzwil,Switzerland) was charged to a 1 qt jar to which was added with stirring,450 g 1-methoxy-2-propanol, 28.5 g Silane A174, 19.16 g Silquest A-1230and 0.5 g of a 5% solution of Prostab 5198 in water. This mixture wasstirred 30 min at room temperature then sealed and heated to 90° C. for3.0 h. The contents of the jars were removed and concentrated toapproximately 40% ZrO₂ via rotary evaporation. Deionized water (707.8 g)and 24.2 g concentrated aqueous ammonia (29% NH₃) were charged to a 4 Lbeaker. The concentrated dispersion (346.8 g) was added slowly to thebeaker with stirring. The white precipitate thus obtained was isolatedvia vacuum filtration and washed with additional D.I. water. The dampsolids were dispersed in 1-methoxy-2-propanol. The resultant silanemodified zirconia dispersion contained 20.58% solids.

The above modified ZrO₂ dispersion (225.2 g), 20/60/20 PEA/FirstMonomer/SR444 (30.9 g) and a 5% solution of Prostab 5198 in water (0.24g) were charged to a 1 L round bottom flask. Water and alcohol wereremoved via rotary evaporation. The resultant formulation contained47.85% ZrO₂ by TGA and had a refractive index of 1.615. 1 wt % TPO-L wasadded.

Example 6

A ZrO₂ sol was prepared according to U.S. patent application Ser. No.11/027,426 filed Dec. 30, 2004 yielding a sol with 45.78% solids. TheZrO₂ was tested according to the following ZrO₂ Test Methods:

Photon Correlation Spectroscopy (PCS)

The volume-average particle size was determined by Photon CorrelationSpectroscopy (PCS) using a Malvern Series 4700 particle size analyzer(available from Malvern Instruments Inc., Southborough, Mass.). Dilutezirconia sol samples were filtered through a 0.2 μm filter usingsyringe-applied pressure into a glass cuvette that was then covered.Prior to starting data acquisition the temperature of the sample chamberwas allowed to equilibrate at 25° C. The supplied software was used todo a CONTIN analysis with an angle of 90 degrees. CONTIN is a widelyused mathematical method for analyzing general inverse transformationproblems that is further described in S. W. Provencher, Comput. Phys.Commun., 27, 229 (1982). The analysis was performed using 24 data bins.The following values were used in the calculations: refractive index ofwater equal to 1.333, viscosity of water equal to 0.890 centipoise, andrefractive index of the zirconia particles equal to 1.9.

Two particle size measurements were calculated based on the PCS data.The intensity-average particle size, reported in nanometers, was equalto the size of a particle corresponding to the mean value of thescattered light intensity distribution. The scattered light intensitywas proportional to the sixth power of the particle diameter. Thevolume-average particle size, also reported in nanometers, was derivedfrom a volume distribution that was calculated from the scattered lightintensity distribution taking into account both the refractive index ofthe zirconia particles and the refractive index of the dispersing medium(i.e., water). The volume-average particle size was equal to theparticle size corresponding to the mean of the volume distribution.

The intensity-average particle size was divided by the volume-averageparticle size to provide a ratio that is indicative of the particle sizedistribution.

Crystalline Structure and Size (XRD Analysis)

The particle size of a dried zirconia sample was reduced by handgrinding using an agate mortar and pestle. A liberal amount of thesample was applied by spatula to a glass microscope slide on which asection of double coated tape had been adhered. The sample was pressedinto the adhesive on the tape by forcing the sample against the tapewith the spatula blade. Excess sample was removed by scraping the samplearea with the edge of the spatula blade, leaving a thin layer ofparticles adhered to the adhesive. Loosely adhered materials remainingafter the scraping were remove by forcefully tapping the microscopeslide against a hard surface. In a similar manner, corundum (Linde 1.0μm alumina polishing powder, Lot Number C062, Union Carbide,Indianapolis, Ind.) was prepared and used to calibrate thediffractometer for instrumental broadening.

X-ray diffraction scans were obtained using a Philips verticaldiffractometer having a reflection geometry, copper K_(α) radiation, andproportional detector registry of the scattered radiation. Thediffractometer was fitted with variable incident beam slits, fixeddiffracted beam slits, and graphite diffracted beam monochromator. Thesurvey scan was conducted from 25 to 55 degrees two theta (20) using a0.04 degree step size and 8 second dwell time. X-ray generator settingsof 45 kV and 35 mA were employed. Data collections for the corundumstandard were conducted on three separate areas of several individualcorundum mounts. Data was collected on three separate areas of the thinlayer sample mount.

The observed diffraction peaks were identified by comparison to thereference diffraction patterns contained within the International Centerfor Diffraction Data (ICDD) powder diffraction database (sets 1-47,ICDD, Newton Square, Pa.) and attributed to either cubic/tetragonal(C/T) or monoclinic (M) forms of zirconia. The (111) peak for the cubicphase and (101) peak for the tetragonal phase could not be separated sothese phases were reported together. The amounts of each zirconia formwere evaluated on a relative basis and the form of zirconia having themost intense diffraction peak was assigned the relative intensity valueof 100. The strongest line of the remaining crystalline zirconia formwas scaled relative to the most intense line and given a value between 1and 100.

Peak widths for the observed diffraction maxima due to corundum weremeasured by profile fitting. The relationship between mean corundum peakwidths and corundum peak position (20) was determined by fitting apolynomial to these data to produce a continuous function used toevaluate the instrumental breadth at any peak position within thecorundum testing range. Peak widths for the observed diffraction maximadue to zirconia were measured by profile fitting observed diffractionpeaks. The following peak widths were evaluated depending on thezirconia phase found to be present:

-   -   Cubic/Tetragonal (C/T): (1 1 1)    -   Monoclinic (M): (−1 1 1), and (1 1 1)        A Pearson VII peak shape model with K_(α1) and K_(α2) wavelength        components accounted for, and linear background model were        employed in all cases. Widths were found as the peak full width        at half maximum (FWHM) having units of degrees. The profile        fitting was accomplished by use of the capabilities of the JADE        diffraction software suite. Sample peak widths were evaluated        for the three separate data collections obtained for the same        thin layer sample mount.

Sample peaks were corrected for instrumental broadening by interpolationof instrumental breadth values from corundum instrument calibration andcorrected peak widths converted to units of radians. The Scherrerequation was used to calculate the primary crystal size.Crystallite Size (D)=Kλ/β(cos θ)In the Scherrer equation,

-   -   K=form factor (here 0.9);    -   λ=wavelength (1.540598 Å);    -   β=calculated peak width after correction for instrumental        broadening (in radians)=[calculated peak FWHM−instrumental        breadth] (converted to radians) where FWHM is full width at half        maximum; and    -   θ=½ the peak position (scattering angle).        The cubic/tetragonal crystallite size was measured as the        average of three measurements using (1 1 1) peak.        Cubic/Tetragonal Mean Crystallite Size=[D(1 1 1)_(area 1) +D(1 1        1)_(area 2) +D(1 1 1)_(area 3)]/3        The monoclinic crystallite size was measured as the average of        three measurement using the (−1 1 1) peak and three measurements        using the (1 1 1) peak.        Monoclinic Mean Crystallite Size=[D(−1 1 1)_(area 1) +D(−1 1        1)_(area 2) +D(−1 1 1)_(area 3) +D(1 1 1)_(area 1) +D(1 1        1)_(area 2) +D(1 1 1)_(area 3)]/6        The weighted average of the cubic/tetragonal (C/T) and        monoclininc phases (M) were calculated.        Weighted average=[(% C/T)(C/T size)+(% M)(M size)]/100        In this equation,    -   % C/T=the percent crystallinity contributed by the cubic and        tetragonal crystallite content of the ZrO₂ particles;    -   C/T size=the size of the cubic and tetragonal crystallites;    -   % M=the percent crystallinity contributed by the monoclinic        crystallite content of the ZrO₂ particles; and    -   M size=the size of the monoclinic crystallites.        Dispersion Index

The Dispersion Index is equal to the volume-average size measured by PCSdivided by the weighted average crystallite size measured by XRD.

Weight Percent Solids

The weight percent solids were determined by drying a sample weighing 3to 6 grams at 120° C. for 30 minutes. The percent solids can becalculated from the weight of the wet sample (i.e., weight beforedrying, weight_(wet)) and the weight of the dry sample (i.e., weightafter drying, weight_(dry)) using the following equation.wt-% solids=100 (weight_(dry))/weight_(wet)

The results were as follows: Intensity-average Size Volume-average SizeIntensity-average:Volume-average (nm) (nm) Ratio ZrO2 42.1 17.5 2.41 SolXRD M Size C/T C/T Size Average Dispersion M Intensity (nm) Intensity(nm) % C/T Size (nm) Index ZrO2 9 6.5 100 8.0 92 7.9 2.21 Sol

The ZrO₂ Sol (50.00 g), MEEAA (2.22 g), BCEA (1.06 g),1-methoxy-2-propanol (75 g), and a 50/50 mix of PEA/RDX (17.60 g) werecharged to a round bottom flask and the alcohol and water were removedvia rotary evaporation. The ZrO₂ containing resin was 49.59% ZrO₂ andhad a refractive index of 1.639. 0.5 pph of TPO-L was added to the abovemixture.

This was prepared into a brightness enhancing film according toExperiment 2 with the exception that the prisms varied in height alongtheir length similar to that of a brightness enhancing film sold by 3MCompany under the trade designation “Vikuiti BEF III 90/50 Film”. Theresults are reported in Table I.

The recitation of numerical ranges by endpoint includes all numberssubsumed within that range (e.g. 1 to 5 includes 1. 1.5, 2, 2.75, 3,3.80, 4 and 5). The complete disclosures of the patents, patentdocuments, and publications cited herein are incorporated by referencein their entirety as if each were individually incorporated. Variousmodifications and alterations to this invention will become apparent tothose skilled in the art without departing from the scope and spirit ofthis invention. It should be understood that this invention is notintended to be unduly limited by the illustrative embodiments andexamples set forth herein and that such examples and embodiments arepresented by way of example only with the scope of the inventionintended to be limited only by the claims set forth herein as follows.

1. A brightness enhancing film having a polymerized structure comprisingthe reaction product of a) at least about 15 wt-% of one or more firstmonomers selected from the group consisting of: i) a monomer comprisinga major portion having the structure

wherein R1 is independently hydrogen or methyl, R2 is independentlyhydrogen or bromine, Q is independently O or S, and Z is independently—C(CH₃)₂—, —CH₂—, —C(O)—, —S—, —S(O)—, or —S(O)₂—; ii) a monomercomprising a major portion having the structure

wherein R1 is independently hydrogen or methyl, R2 is independentlyhydrogen or bromine, Q is independently O or S, Z is independently—C(CH₃)₂—, —CH₂—, —C(O)—, —S—, —S(O)—, or —S(O)₂, and L is a linkinggroup independently selected from linear or branched C₂-C₁₂ alkyl groupswherein the carbon chain is optionally substituted with one or moreoxygen group and/or the carbon atoms are optionally substituted with oneor more hydroxyl groups; and mixtures of i and ii; b) at least about 10wt-% of inorganic nanoparticles; c) optionally a crosslinking agent. 2.The brightness enhancing film of claim 1 wherein the compositioncomprises photoinitiator.
 3. The brightness enhancing film of claim 1wherein the amount of inorganic particles is less than about 60 wt-%. 4.The brightness enhancing film of claim 1 wherein the inorganicnanoparticles are surface modified.
 5. The brightness enhancing film ofclaim 1 wherein the inorganic nanoparticles comprise silica, zirconia,titania, antimony oxides, alumina, tin oxides, mixed metal oxidestherof, or mixtures thereof.
 6. The brightness enhancing film of claim 1wherein the primary particle ranges in size from 5 nm to 75 nm, 10 nm to30 nm, or 5 nm to 20 nm.
 7. The brightness enhancing film of claim 1wherein the first monomer consists of the reaction product ofTetrabromobisphenol A diglycidyl ether and (meth)acrylic acid.
 8. Thebrightness enhancing film of claim 1 wherein the crosslinking agent is aliquid at ambient temperature.
 9. The brightness enhancing film of claim1 wherein the crosslinking agent is multi functional urethane(meth)acrylate crosslinker.
 10. The brightness enhancing film of claim 1wherein the crosslinking agent is selected from the group consisting ofhexanediol diacrylate, pentaerythritol tri(meth)acrylate,pentaerythritol tetra(meth)acrylate, trimethylolpropanetri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate,dipentaerythritol penta(meth)acrylate, hexanediol diacrylate, andmixtures thereof.
 11. The brightness enhancing film of claim 1 furthercomprising at least one monofuntional or difunctional ethylenicallyunsaturated diluent.
 12. The brightness enhancing film of claim 10wherein the diluent is a liquid at room temperature.
 13. The brightnessenhancing film of claim 11 wherein the diluent comprisesphenoxyethyl(meth)acrylate, benzyl(meth)acrylate, N-vinyl pyrrolidone,and N-vinyl caprolactam.
 14. The brightness enhancing film of claim 11wherein the diluent comprises N-substituted or N,N-disubstituted(meth)acrylamides.
 15. The brightness enhancing film of claim 1 whereinthe polymerizable composition is free of methacrylate functionalmonomer.
 16. The brightness enhancing film of claim 1 wherein the filmis a turning film optionally comprising rounded apexes having a radiusof 0.5 to 10 micrometers.
 17. An article comprising the brightnessenhancing film of claim 1 and a second optical film in contact with thebrightness enhancing film.
 18. The article of claim 17 wherein thesecond optical film is selected from the group comprising a turningfilm, a diffuser, an absorbing polarizer, a reflective polarizer, and aprotective cover film.
 19. The article of claim 18 wherein the secondoptical film comprises a prismatic structure.
 20. A brightness enhancingfilm having a polymerized structure comprising the reaction product of apolymerizable composition comprising a) at least about 15 wt-% of one ormore (meth)acrylated aromatic epoxy oligomers; b) at least about 10 wt-%inorganic nanoparticles; and c) optionally a crosslinking agent.
 21. Apolymerizable resin composition comprising a) at least about 15 wt-% ofone or more first monomers selected from the group consisting of: i) amonomer comprising a major portion having the structure

wherein R1 is independently hydrogen or methyl, R2 is independentlyhydrogen or bromine, Q is independently O or S, and Z is independently—C(CH₃)₂—, —CH₂—, —C(O)—, —S—, —S(O)—, or —S(O)₂—; ii) a monomercomprising a major portion having the structure

wherein R1 is independently hydrogen or methyl, R2 is independentlyhydrogen or bromine, Q is independently O or S, Z is independently—C(CH₃)₂—, —CH₂—, —C(O)—, —S—, —S(O)—, or —S(O)₂—, and L is a linkinggroup independently selected from linear or branched C₂-C₁₂ alkyl groupswherein the carbon chain is optionally substituted with one or moreoxygen group and/or the carbon atoms are optionally substituted with oneor more hydroxyl groups; and mixtures of i and ii; b) at least about 10wt-% of inorganic nanoparticles; c) optionally a crosslinking agent; andd) optionally a photoinitiator.
 22. An optical article comprising thereaction product of claim
 21. 23. The optical article of claim 22wherein the material is a film optionally having a microstructuredsurface.
 24. The optical article of claim 24 wherein the microstructuredsurface comprises cube corner structures or structures suitable formaking barrier ribs for a plasma display panel.
 25. The brightnessenhancing film of claim 1 wherein the structure comprises a plurality ofridges having rounded apexes having a radius ranging from 4 to 15micrometers.
 26. A brightness enhancing film comprising: a brightnessenhancing polymerized structure comprising the reaction product of asubstantially solvent free polymerizable composition comprising anorganic component comprising one or more ethylenically unsaturatedmonomers wherein the organic component has a viscosity of less than 1000cps at 180° F.; and at least 10 wt-% inorganic nanoparticles.
 27. Thebrightness enhancing film of claim 26 wherein the organic component hasa viscosity of less than 1000 cps at 180° F., a viscosity of less than1000 cps at 160° F., a viscosity of less than 1000 cps at 140° F., aviscosity of less than 1000 cps at 120° F., a viscosity of less than 800cps at 120° F., or a viscosity of less than 600 cps at 120° F.
 28. Thebrightness enhancing film of claim 26 wherein the organic componentcomprises at least one (meth)acrylated urethane oligomer,(meth)acrylated polyester oligomer, (meth)acrylated phenolic oligomer,(meth)acrylated acrylic oligomer, (meth)acrylated epoxy(meth)acrylateand mixture thereof.
 29. The brightness enhancing film of claim 26wherein the organic component comprises at least one oligomericethylenically unsaturated monomer having a number average molecularweight of at least 450 g/mole.
 30. A brightness enhancing filmcomprising: a brightness enhancing polymerized structure comprising thereaction product of a substantially solvent free polymerizablecomposition comprises an organic component comprising one or moreethylenically unsaturated monomers wherein the organic component has arefractive index of at least 1.54; and at least 10 wt-% inorganicnanoparticles.
 31. The brightness enhancing film of claim 30 wherein thepolymerizable composition has a refractive index of at least 1.47, arefractive index of at least 1.52, a refractive index of at least 1.55,or a refractive index of at least 1.60.